title: The anovulatory hamster: a comparison of the effects of short photoperiod and daily melatonin injections on the induction and termination of ovarian acyclicity.
abstract: Cyclic female hamsters were rendered anovulatory by daily subcutaneous melatonin injections (25 microgram/0.1 ml oil) in 29 days or by transfer to a short light cycle, LD 6:18 (lights 1000-1600 hrs) in 33 days. Estrous cyclicity was reinitiated in these animals in 44 or 45 days following cessation of melatonin injections or transfer to long light cycles (LD 14:10, lights 0600-2000 hrs), respectively. Exposure of both groups to LD 6:18 after reinitiation of estrous cyclicity caused a second cessation of ovulation in 75 (melatonin group) or 61 (short light cycle group) days. Thus, although both treatments disrupted estrous cyclicity for nearly 6 weeks, this was not sufficient to induce photorefractoriness (failure to respond to short light cycles with continued estrous cyclicity). Rather, every animal responded to LD 6:18 and ceased ovulating. Melatonin-induced anovulatory hamsters showed daily gonadotropin release patterns identical to those reported in hamsters in other anovulatory states (lactating, prepubertal, and photoinduced anovulatory hamsters); that is, peak LH and FSH release at 1700 hrs daily.
mesh_terms: D000818:Animals; D006224:Cricetinae; D004971:Estrus; D005260:Female; D005640:Follicle Stimulating Hormone / Q000097:blood; D008027:Light; D007986:Luteinizing Hormone / Q000097:blood; D008550:Melatonin / Q000494:pharmacology; D008647:Mesocricetus; D010053:Ovary / Q000502:physiology*; D010060:Ovulation / Q000187:drug effects / Q000528:radiation effects*; D011247:Pregnancy; D013997:Time Factors
chemical_list: D007986:Luteinizing Hormone; D005640:Follicle Stimulating Hormone; D008550:Melatonin